Project Summary Cardiovascular disease is the leading cause of death in the United States. Clinical therapies currently available for heart failure are limited and do not provide a viable strategy to restore blood flow to a large group of patients. Consequently, the survival in this patient population is severely limited. Experimental therapies have attempted to restore circulation to threatened heart muscle using stem cells to regenerate micro-circulation. While this strategy demonstrated promise in experimental settings, translation to clinical therapy has been limited by a lack of significant benefit, due to cell death and a lack of retention (<1%). The therapeutic benefit of stem cells appears to be largely related to paracrine mechanisms (the proteins secreted by the cells) rather than the cells themselves. Exosomes appear to be at the center of paracrine signaling. Exosomes are vesicles secreted by the cells that contain cell signaling molecules that play an important role in cell survival, replication, and formation of vessels. They are particularly attractive for therapy, when compared to cells, in that they are easily harvested in large quantities, can be frozen and stored indefinitely, and rapidly prepared for therapy. Unfortunately, retaining the exosomes in the heart with just injection is a challenge. In order to overcome these limitations, we have developed a novel shear thinning hydrogel to allow delivery and retention of exosomes in the heart. This novel hydrogel is able to liquefy under shear forces, enabling injection through a syringe, and immediately reforming upon elimination of the shear stress. The properties of the gel facilitate optimal exosome delivery (98%) with minimal loss. We hypothesize that delivery of exosomes within the shear thinning hydrogel will enable efficient delivery to compromised heart muscle with excellent retention. We will identify factors secreted by the exosomes and gain an understanding of the pathways involved in therapy. We will also evaluate optimal timing, relative to myocardial infarction (heart attack) for delivery of the exosomes. Additionally, we will translate therapy to a sheep model of heart failure, as a preclinical assessment.